At lateral collisions the sill of a car is exposed to large stress, since they are often exposed to direct collision forces from the colliding vehicle. Since the forces also influences parts of the car body higher up, a torsional moment is generated, which makes the sill beam and the lateral beam to twist upwards, inwards. The car body therefore does not constitute the protection against lateral collisions as would be desireable.
The problem has been observed in many quarters and now there is detailed legislation relating to how large forces the car body should be able to absorb from the side. In order to counteract the above mentioned torsional tendencies, there have been attempts to among others inject isocyanates in the sill beam. This however gives problem with moisture and thereby corrosion in the long run.
It is previously known by self-supporting car bodies to arrange hollow beams, which are made rigid by transverse frames and/or diagonal frames inside the hollow beam. These beams in fact are effective, but increases the weight of the vehicle with quite a number of kilos, which cannot be accepted today. The division of hollow beams into a number of smaller cells also leads to an increasing risk for corrosion.